Dual-use visible-light/infrared image pickup device

Abstract

A shift in focal point due to longitudinal chromatic aberration of a photographing lens is properly corrected in accordance with various photographing conditions, by means of controlling the thickness of a variable-thickness optical filter interposed between an image pickup lens system and a solid-state image pickup element, on the basis of a correlation table defining the correlation between photographing conditions and the thickness of the variable-thickness optical filter that can correct a shift in focal point. A variable-thickness optical filter is interposed between a photographing lens system and a CCD having sensitivity ranging from the visible-light range to the infrared range. The thickness of the optical filter is changed, by means of controlling an actuator on the basis of a correlation table defining the correlation between the photographing conditions and the thickness of the variable-thickness optical filter which can correct the shift in optical focal point. The variable-thickness optical filter is formed from two wedge-shaped prisms combined together to form a parallel-plane plate, and the overall thickness of the variable-thickness optical filter can be changed, by means of moving the prisms in opposite directions while oblique lines of the prisms remain in contact with each other.

What is claimed is:  
     
         1 . A dual-use visible-light/infrared image pickup device including an image pickup element having sensitivity ranging from the visible-light range to the infrared range and means for correcting a shift in focal point, which would otherwise be caused by longitudinal chromatic aberration arising in a photographing lens, the device comprising: 
 a variable-thickness optical filter interposed between a photographing lens system and said image pickup element of solid state;    an actuator for changing the thickness of said variable-thickness optical filter;    memory for storing a correlation table defining the correlation between said photographing conditions and the thickness of said variable-thickness optical filter which can correct said shift in optical point; and    thickness control means for controlling said actuator on the basis of said correlation table stored in said memory.    
     
     
         2 . The dual-use visible-light/infrared image pickup device according to    claim 1   , wherein said variable-thickness optical filter is formed from two wedge-shaped prisms combined together to form a parallel-plane plate, and the overall thickness of said variable-thickness optical filter can be changed, by means of moving said prisms in opposite directions while oblique lines of said prisms remain in contact with each other.  
     
     
         3 . The dual-use visible-light/infrared image pickup device according to    claim 1   , wherein said variable-thickness optical filter is constructed such that the overall thickness of said variable-thickness optical filter can be changed by means of shifting liquid filled in the space defined between the two parallel plates.  
     
     
         4 . The dual-use visible-light/infrared image pickup device according to    claim 1   , wherein the photographing conditions correspond to at least one of the wavelength of incident light, the brightness of said photographing lens system, the brightness of a subject, a zoom magnification, a focal point, and the aperture of a diaphragm.  
     
     
         5 . The dual-use visible-light/infrared image pickup device according to    claim 1   , wherein said photographing lens is a zoom lens.  
     
     
         6 . The dual-use visible-light/infrared image pickup device according to    claim 1   , wherein said photographing lens is a fixed-focus lens.  
     
     
         7 . The dual-use visible-light/infrared image pickup device according to    claim 1   , wherein said image pickup device is a monitoring camera.